1. Field of the Invention
The present invention is related to the field of single and multiple-wall carbon nanotubes. More precisely, the present invention is related to hydroxide and carbonate-based supported catalysts for carbon nanotube preparation.
2. Description of the Related Art
Carbon nanotubes were first observed by Iijima in 1991 (S. Iijima, Nature 354, 56-58 (1991)).
Carbon nanotubes can be produced for example, by arc discharge, by laser ablation or by catalytic decomposition of hydrocarbons.
The production of carbon nanotubes by the arc discharge and the laser ablation techniques can be carried out either in the absence of catalysts to produce multi-wall nanotubes (MWNTs) or in the presence of catalysts to produce both MWNTs and single-wall nanotubes (SWNTs), together with soot, amorphous carbon and encapsulated metal nanoparticles. The catalyst comprises generally metals, metal oxides or other metal derivatives or mixtures thereof. Examples of those metals are i.e., Co, Fe, Ni, V, Mo, Sn, . . . .
The invention discloses the preparation of carbon nanotubes by the catalytic decomposition of hydrocarbons, a technique called CCVD (Catalytic Carbon Vapour Deposition), carried out in the presence of catalysts to produce both MWNTs and SWNTs. Soot and encapsulated metal nanoparticles are the other by-products. The hydrocarbon can be acetylene, ethylene, butane, propane, ethane, methane or any other gaseous or volatile carbon containing compound. The catalyst, for example transition metal, is generally, either pure or dispersed on a support.
The presence of a support for the catalyst affects the activity of the catalysts tremendously in the formation of carbon nanotubes. The selectivity of the catalyst for the production of nanotubes also depends on the type of catalyst support interaction.
The most common supports used to prepare supported catalyst for carbon nanotubes production are oxides [i.e., silica (P. Piedigrosso et al., Phys. Chem. Chem. Phys. 2, 163-170 (2000)), alumina (I. Willems et al., Chem. Phys. Lett. 317, 71-76 (2000)), silica-alumina mixtures (Kukovecz, A. et al., Phys. Chem. Chem. Phys. 2, 3071-3076 (2000)), magnesium oxide (J.-F. Colomer et al., Chem. Phys. Lett. 317, 83-89 (2000)), calcium oxide (C. Ping et al., CN 1170631 A 19980121), titanium oxide (V. Curtis, et al., Book of Abstracts, 219th ACS National Meeting, San Francisco, Calif., Mar. 26-30, 2000), cerium oxide (L. Ji et al., Appl. Chem. 72, 327-331 (2000)), zeolites (K. Hernadi et al., Zeolites 17, 416-423 (1996)), lays (A. Fonseca et al., Appl. Phys. A 67, 11-22 (1998)), spinels (A. Govindaraj et al., J. Mater. Res. 14, 2567-2576 (1999)), ALPOs (Wang, N. et al., Nature 408, 50-51 (2000))] and graphite (V. Ivanov et al., Carbon 33, 1727-1738 (1995)).
The use of porous materials (i.e., silica, alumina, zeolites, etc.) as supports for catalysts, contaminates the carbon nanotubes produced thereon with a large amount of soot and amorphous carbon, while dissolving the support during the purification of the carbon nanotubes.
The catalyst supports used in the present invention do not present the drawbacks of the catalyst supports of the state of the art.
The document of Dujardin E. et al., Solid state communications (2000), Elsevier USA, vol. 14, no. 10, pp. 543-546, is related to the synthesis of single shell carbon nanotubes using catalysts such as Co, Ni and mentions the presence of remaining interstitial metallic residues in purified single shell carbon nanotubes, even after prolonged treatments in boiling concentrated HNO3.
The document of Cassell A. M. et al., J. Phys. Chemistry B. (1999), vol. 103, no. 31, pp. 6484-6492, discloses large scale CVD synthesis of single-walled carbon nanotubes using different catalysts with different metal compounds and/or different support materials. The optimized catalysts consist in Fe/Mo bimetallic species supported on a silica-alumina multicomponent material.
The document of Biro L. P. et al., Materials Science and Engineering (2002), vol. C19, pp. 9-13, Elsevier USA, is related to multiwall carbon nanotubes grown by the catalytic decomposition of acetylene over supported Co catalyst and subjected to wet and dry oxidation in order to remove unwanted products and catalytic traces. KMnO4/H2SO4 aqueous oxidation procedure was found to be effective in reducing the Co content while damaging only moderately the outer wall of the nanotubes.
Documents XP-002197395 (Database WPI, Derwent Publications Ltd, London, GB) & RU 2 135 409 C of 27 Aug. 1999, are related to layered carbon nanotubes, hollow and/or metal-filled, obtained from a mixture of carbon-chain polymer and high molecular carbocyclic or heterocyclic compound with iron-, cobalt-, or nickel-containing substance such as hydroxide, oxide, salt, organometallic compound, or carbonyl, heated to 600-1000° C. under inert gas (nitrogen, helium, argon, xenon, krypton) atmosphere in the form of gas stream or static medium, wherein the geometric parameters and the number of metal inclusions are controlled.
The document of Che G. et al., Chem. Mater. (1998), vol. 10, pp. 260-267, discloses a method for preparing graphitic carbon nanofiber and nanotube ensembles. This method entails chemical vapor deposition based synthesis of carbon within the pores of an alumina template membrane with or without a Ni catalyst. Ethylene or pyrene was used in the chemical vapor deposition with reactor temperatures of 545° C. for Ni-catalyzed method and 900° C. for uncatalyzed method. The resultant carbon nanostructures were found to be uniform hollow tubes with open ends.
The document of Fonseca A. et al., Appl. Phys. (1998), vol. 67, pp. 11-22, discloses catalytic synthesis of single- and multi-wall carbon nanotubes using supported transition-metal catalysts. Said catalysts were prepared by different methods and tested in the production of nanotubes by decomposition of hydrocarbon at 700° C., using a fixed-bed flow reactor.
The document of Sinha A. K. et al., Chem. Phys. Lett. (2000), vol. 332, pp. 455-460, discloses the large-scale production of carbon nanotubes filled with metal by a catalytic chemical vapor deposition method using a microporous aluminophosphate support and presents said support as an alternative to Na—Y zeolite support.
Document WO 00/17102 is related to a process for producing single-wall carbon nanotubes using a catalyst-support system which, under certain experimental conditions, promotes the growth of single-wall carbon nanotubes in a specific size-range rather than the growth of large irregular-sized multi-walled carbon fibrils.
Document EP-A-0 619 388 discloses a non-aqueous metal catalyst comprising iron and at least one element chosen from Groups V, VI or VII or the lanthanides, for preparing carbon fibrils, particularly carbon fibrils having a morphology consisting of vermicular tubes that are free of a continuous thermal carbon overcoat and have graphite layers that are substantially parallel to the fibril axis.
Documents XP-002197396 (Database WPI, Section CH, Week 198237, Derwent Publications Ltd., London, GB) and JP-A-57127449 concern a method for producing a colloidal metal compound supported catalyst, said method comprising contacting a colloidal metal compound with a powder consisting of alkaline earth metal salt in the absence of a protective colloid, and thereby supporting the colloidal metal compound on the powder.
U.S. Pat. No. 5,982,102 discloses a catalyst for the production of carboxylic acid esters for use in reacting an aldehyde with an alcohol in a liquid phase in the presence of molecular oxygen, said catalyst comprising calcium carbonate and palladium, bismuth and at least one element selected from the group consisting of barium, iron, zinc and germanium, these elements being supported on said calcium carbonate.